A semiconductor chip or a semiconductor device is used while being mounted on an alloy for heat dissipation in order to prevent an abnormal rise in temperature due to heat generation during operation. The alloy for heat dissipation may be referred to as a heat sink or a heat spreader. Examples of methods for mounting the semiconductor chip or the semiconductor device on the alloy for heat dissipation include (1) a method of soldering or brazing directly, (2) a method of soldering or brazing via ceramic, e.g., aluminum nitride (AlN), and (3) a method of mounting with a thermal conductive resin, e.g., silicone grease, interposed therebetween. In every case, the alloy for heat dissipation is required to have a high thermal conductivity in order to promptly dissipate the heat generated from the semiconductor chip or the semiconductor device during operation.
In the methods of the above-described items (1) and (2), the semiconductor chip or aluminum nitride substrate is firmly mounted on the alloy for heat dissipation. Therefore, in order to prevent, for example, cracking of solder layer and warpage, an alloy for heat dissipation having a thermal expansion coefficient close to that of the semiconductor and, furthermore, that of the ceramic, e.g., aluminum nitride, is required.
It is difficult to achieve the above-described characteristics by a simple raw material. Heretofore, in general, so-called composite materials, in which a material having a small thermal expansion coefficient and a material having a large thermal conductivity are combined, have been used frequently as the alloy for heat dissipation. In Patent Document 1, metal-metal based composite materials, e.g., tungsten-copper (W—Cu) and molybdenum-copper (Mo—Cu), have been proposed. The above-described proposal has been made because tungsten and molybdenum have low thermal expansion coefficient, on the other hand, copper has a high thermal conductivity. In Patent Document 2, ceramic-metal based composite materials, e.g., silicon carbide-aluminum (SiC—Al) and cuprous oxide-copper (Cu2O—Cu), are disclosed. Furthermore, in Patent Document 3, metal-metal based composite materials, e.g., chromium-copper (Cr—Cu) and niobium-copper (Nb—Cu), have been proposed.
On the other hand, in the case where the semiconductor device is mounted on the heat dissipation material with a thermal conductive resin, e.g., silicone grease, interposed therebetween, the difference in thermal expansion between the semiconductor chip or aluminum nitride substrate and the heat dissipation plate is absorbed by the thermal conductive resin and, thereby, inexpensive alloys for heat dissipation, e.g., pure copper exhibiting large thermal expansion, can be used. However, since the thermal conductivity of the resin is small as compared with the solder or braze, it is undesirable to use for the semiconductor chip and semiconductor device having a high heating value.
The chromium copper (JIS-Z3234) alloy used as an electrode material for welding from long ago is a precipitation hardened alloy, and is also used as an alloy for heat dissipation in place of the pure copper in the use in which strength is required. However, the thermal expansion coefficient thereof is substantially the same as that of the pure copper and is a high 17.6×10−6/K. Consequently, it cannot be applied as an alloy for heat dissipation to be subjected to soldering or brazing.
Patent Document 1: Japanese Examined Patent Application Publication No. 5-38457
Patent Document 2: Japanese Unexamined Patent Application Publication No. 2002-212651
Patent Document 3: Japanese Unexamined Patent Application Publication No. 2000-239762